Stefano, I think you are in better shape than you think. Most women are jelaous, but also posessive and they like conquests just like we do. So, the fact that there are women around you went out with may make her a little bit jelaous but also a little bit posessive. the fact that you chose her over the other ones you dated will give her a feeling of accomplishment. I would be rather matter-of-factly about it. if she asks you tell her the truth and end with a subtle compliment, so she knows you think of her more highly than about the others. You'll see.
BTW, my wife and I met on the net 4 years ago. Married within 12 month and 2 days and now have a 3-year old I just put to sleep.

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1985 190D 2.2l Sold-to Brother-in-law
1996 Mustang 3.8l -"thinks it's a sports car"
1988 Grand Wagoneer - Sold (good home)
1995 Grand Cherokee Ltd -"What was I thinking??!!"